2780 J. Org. Chem., Vol. 44, No. 15, 1979
Russell et al.
Aliphatic Semidiones. 39. Cyclononane-1,2-semidione and Derivatives' Glen A. Russell,* C. E. 0such,2 G. Senatore, T. Morita, and M. Yamashita Department of Chemistry, Iowa State University, Ames, Iowa 50011 Received January 29, 1979
Cyclononane-1,2-semidioneexists as the (2)isomer with a preferred chair-like conformation. Ring inversion has been detected by ESR spectroscopy with AH*= 5 kcal/mol and AS* = -15 eu. 6,6-Dimethyl-6-silacyclononane-1,2-semidione exists as ( E )and (2)isomers. For the free ions, the ( E )isomer is the preferred structure, but in the presence of K+, the (2)isomer is more stable because of ion pairing. The (2)isomer gives ring inversion with LW = 2.3 kcal/mol and AS* = -23 eu. The ( E )isomer at low temperatures exists as a pair of superimposable conformations possessing four different a-hydrogen atoms which are time averaged at +50 "C to give an ESR spectrum with hyperfine splitting from two pairs of a-hydrogen atoms. The ( E )isomer does not undergo internal rotation (which would make all four a-hydrogen atoms equivalent) up to 110 "C.
We have previously reported that cyclobutane- and cyclopentane-1,2-semidionesgive no evidence of conformational motion by ESR s p e c t r o ~ c o p y ,that ~ ~ ~cyclohexane-1,2-semidione exists as a half-chair conformation with AH* for ring inversion = 4.0 kcal/m01,~and that cycloheptane-l,2-~emidione exists as a frozen staggered conformation (1)in the ESR time frame (7 > lo4 s at 100
Chart I. Ring Inversion of Cyclic 1,2-Semidiones, AH* in kcal/mol, T , = coalescence temperature (* 5 "C), A S * in cal/(" C mol) (K' Counterion in All Cases)
&Po. DMF
d
-0
,.0
1, a H in G g = 2.00482
2, a H in G g=
2.00493
oC).6 The paramagnetic 1,2-semidiones appear to be reasonable conformational models for the parent olefins. Cyclooctane-1,2-semidione(and the larger even-membered ring semidiones) is conformationally complex, but a t +50 "C the four a-hydrogen atoms are time averaged in the ESR measurement. Cyclononane-l,2-~emidione (2) is of considerable interest because of the possibility of observing a cyclic trans-1,Bsemidione. However, we have found no evidence for the ( E ) isomer of 2. From -30 to +50 "C, 2 is conformationally stable as judged by the rich hyperfine (hf) structure of the ESR spectrum (Figure la). At higher temperatures, the ESR spectrum of 2 is a triplet of triplets from the a-hydrogen atoms which coalesces (Figure l b ) to a quintet above 115 " C (the highest temperature at which the a-axial and a-equatorial hyperfine splitting (hfs) can be visually resolved). From peak separation as a function of temperature, AH* for ring inversion of 2 is 5.0 kcal/mol (Chart I, an error limit of A0.3 kcal/mol in LWand A0.5 eu in AS*results if the rate constants measured are in error by a factor of 2). In a similar fashion, the 5,5-dimethyl-5-sila derivative of 1 gave a coalescence of the a-hydrogens at +70 "C with AH* = 6.3 kcal/mol (Chart I).7 The silacycloalkane-1,2-semi(1)Application of ESR Spectroscopy to Problems of Structure and Conformation. 32. This work was partially supported by a grant from the Petroleum Research Fund, administered by the American Chemical Society. Grateful acknowledgement is made to the donors of this fund. (2) N.S.F. Predoctoral Fellow, 1977-1979. (3) G. A. Russell, P. R. Whittle, R. G. Keske, G. Holland, and C. Aubuchon, J . Am. Chem. SOC.,94, 1693 (1972). (4) G. A. Russell, E. R. Talaty, and R. H. Horrocks, J . Org. Chem.,32, 353 (1967). (5) G. A. Russell, G. R. Underwood, and D. C. Lini, J. Am. Chem. SOC., 89, 6623 (1967). (6) G. A. Russell, R. G.Keske, G. Holland, J. Mattox, R. S. Givens, and K. Stanley, J . Am. Chem. SOC.,97, 1892 (1975).
AH* =
6.3; T,= +70; AS'
= -7.0
0-
AH' = 5.0; T, > 115; A S * = - 1 5
AH* = 2.3; Tc > 120; A S * = -23
diones have conformational stabilities roughly equivalent to the carbocyclic analogues with two more atoms in the ring. The two largest hfsc's in 2 were assigned to the a equatorial and axial hydrogen atoms (C-3,9) on the basis of the synthesis of 3 (4,4,8&tetramethylcyclononane-
3, a H in G
1,2-semidione). The staggered conformation of 2 was assigned on the basis of the similarity of the hfsc a t the p, y,and 6 positions with 1,and on the basis of predictions made on the zigzag or W-plan rule for long range h f s c ' ~ . ~ ~ * ~ ~ The assigned hfsc's for 2 are in agreement with the hfsc's (7) G. A. Russell, C. E. Osuch, and W. Chau, Heterocycles, 11,165(1978). (8) G. A. Russell and K.-Y. Chang, J. Am. Chem. Soc., 87 4381 (1965); G. A. Russell, K.-Y. Chang, and C. Jefford, ibid., 87, 4383 (1965). (9) G. A. Russell, G. W. Holland, K.-Y. Chang, R. G. Keske, J. Mattox, C. S. C. Chung, K. Stanley, K. Schmitt, R. Blankespoor, and Y . Kosugi, J . Am. Chem. SOC., 96, 7237 (1974).
0022-3263/79/ 1944-2780$01.00/0 0 1979 American Chemical Society
Cyclononane-l,2-~emidione and Derivatives
J. Org. Chem., Vol. 44, No. 15, 1979 2781 Chart 11. Polycyclic Semidiones Containing a Nine-Membered Ring in the Staggered Configuration ( A ) (Hyperfine Splitting Constants in G )
p
(b)
i'
-
1
01
5
I
10
GAUSS
Y
I
1090)
(6 80)
6b
7
BC Q
Reference 3.
Reference 6.
Reference 9.
Figure 1. Ring inversions of cyclononane-l,2-semidione observed by ESR spectroscopy in Me2S0, K+ counterion. (a) Spectrum at 30 "C showing triplet, triplet, sextet splitting. (b) Spectrum with selective line broadening at +70 "C. (c) Spectrum at +lo0 "C, slightly below coalescence point. (d)Spectrum at +125 "C, slightly above the coalescence temperature.
Chart 111. Polycyclic Semidiones Containing the Nine-Membered Ring in Configuration B (Hyperfine Splitting Constants in G )
in a series of rigid polycyclic semidiones where the nine-membered ring is constrained to conformations A-D.
H\ (1.56)
(0 23)
(0 15)
H (47) 0-
HH
H(O 50)
H (0 50) /
9
H H ( 0 23) 10
A
B
\
Chart IV. Polycyclic Semidiones Having the Nine-Membered Ring in Sickle Conformation (C) (Hyperfine Splitting Constants in G
Hw ( 0 22)H
H
C
U
Chart I1 lists mainly previously described semidiones possessing a nine-membered ring in conformation A. From these model compounds, it is clear that equatorial hydrogen atoms a t the p-, y-, or &carbon atoms (C(4)-C(6)) have larger hfsc's than axial hydrogen atoms a t these positions. Chart I11 lists two semidiones possessing the ninemembered ring in conformation B. No doublet hfs is observed for the d-hydrogen atom of the nine-membered ring as is observed for 1. Chart IV lists two semidiones in which the ninemembered ring possesses structure C. Structure C is also present in the semidione 6 of Chart I. Again, no hfs is noted for the d-hydrogen atom. Chart V gives two structures, one rigid and one conformationally mobile, which possess structure D. Here, hfs can be observed for one or both d-hydrogen atoms in the nine-membered ring. The 6,6-dimethyl-6-sila derivative of 2, prepared from the a-hydroxy ketone plus potassium dimsylate in Me2S0,
(0 16)H
1* $:)( 056(274)H
0-
H
H H (039)H
H
(9 2) ( 1 1)
(10 75)
12b
1lQ
References 3 and 6.
Reference 9.
gave a mixture of semidiones (Figure 2a) which we have identified as the (E) and (2) isomers 15 and 16.
15, aH in G g = 2.00494
16 g = 2.00507
2782 J. Org. Chem., Vol. 44, No. 15, 1979
Russell et al.
Chart V. Polycyclic Semidiones Containing the Nine-Membered Ring in the Cup Configuration ( D ) (Hyperfine Splitting Constants in G ) H
(855)
(1.35)
1 3a
Reference 9. 7e
1
, -o
5 GAUSS
lo
I
Figure 3. ESR spectra of (E)-6,6-dimethyl-6-silacyclononane1,2-semidionein DMF: (a) +80 "C showing a time averaged triplet of triplets; (b) -20 " C showing a sharp 1:2:1 triplet with other lines broadened. 14a U H = 6.90 (Ha), 0.88 (Hb), 2.68 (Hc), 1.68 (Hd), 0.38 (He)
Figure 2. ESR spectra of the mixture of (E)- and (2)-6,6-dimethyl-6-silacyclononane-1,2-semidione at 25 "C in Me2SO: (a) mixture of isomers observed with 0.1 M K+; (b) mainly 2 isomer observed with KI added (c) E isomer observed upon the addition of an excess of [2.2.2]cryptand. The structural assignments hinge partially upon the effect of ion pairing upon g values'O and the greater (10) G. A. Russell and C. E. Osuch, J. Am. Chem. SOC.,100,5979 (1978).
tendency of a cis-1,2-semidione than of a trans-1,2-semidione to undergo ion pairing with Li+, Na+, or K+." Cyclononane-l,2-~emidione itself in the presence of excess K+gives the ion pair with g = 2.00493, aHa= 5.28 (2 H), 2.18 (2 H) G. In the presence of an excess of [2.2.2]cryptand, the free ion is observed with g = 2.00513, aHa = 5.10 (2 H), 2.14 (2 H)G. The two radical ions observed with the 6,6-dimethylsila derivative have different g values suggesting a cis and a trans structure. Addition of excess K+favors one of these species to which we ascribe the cis structure (15, g = 2.00494, Figure 2b). Treatment of the solution with an excess of [2.2.2]cryptand gives mainly the other isomer which we assign as the trans isomer (16, g = 2.00507, Figure 2c). At 25 "C, 15 gives an ESR spectrum with uHa = 7.35 (axial), 1.40 (equatorial) and aHg= 0.48 (equatorial) G. Upon warming, the peaks of the triplet of triplets for the a hydrogens shift and approach a pentet from four equivalent (time averaged) a-hydrogen atoms. From the shifts in the position of the peaks, a AH*for ring flip of 15 of 2.3 kcal/mol can be calculated (Chart I, an error limit of f0.3 kcal/mol and f0.5 eu results if the rate constants measured are in error by a factor of 2). Chart I shows the expected variation in AH* and A S for the ring inversions of the seven- and nine-membered rings. Increasing ring size lowers AH*but makes A S more negative. The floppy large rings have a very low energy barrier for ring flip, but to avoid nonbonded interactions the configurational pathway is a tortuous one of low probability involving rotations among the single bonds in the ring in a rigid time sequence. Addition of [2.2.2]cryptand converts 15 to 16. A transient spectra (apparently when a very slight deficiency of the cryptand was employed) for the free ion of the (2) semidione was detected with g = 2.00507 and aHa = 6.47 (2 H), 1.45 (2 H), aHg= 0.37 (2 H), aHy= 0.16 (2 H)G. For the ion pair 15, aHycould not be resolved. Conformational motion can be detected for 16 also. Above 50 "C, the hfs pattern is a triplet of triplets (aH= 2.3,3.6 G) from the a-hydrogen atoms (Figure 3a). Upon cooling, selective line broadening is observed, and at -30 "C only the wing peaks and center line remain sharp to give a 1:2:1 triplet (Figure 3b). This behavior is also observed for the trans-1,2-semidiones in the 11-,13-, and 15-membered carbocyclic rings. Heating 16 to 110 "C does (11)G. A. Russell, D. F. Lawson, H. L. Malkus, R. D. Stephens, G. R. Underwood, T. Takano, and V. Malatesta, J . Am. Chem. SOC.,96, 5830 (1974); G. A. Russell, G.Wallraff, and J. L. Gerlock, J . Phys. Chem., 82, 1161 (1978).
Cyclononane-l,2-~emidione and Derivatives
not give any indication that all four of the a-hydrogen atoms are being time averaged, and we conclude that internal rotation (eq 1)for 16 must be quite a high-energy
process ( 7 > loa s a t 110 'C). The low-temperature conformational equilibrium observed for 16 and other trans ~yclic-1,2-semidiones~~ excludes structures 16A and 16B or their time average. In structures 16A-D the four chemically and magnetically different kinds of hydrogen atoms are labeled H1-H4. Equilibrium between 16A and 16B would maintain sharp r
---.
16A H , is in the nodal plane of
the
'il
16B H, is i n the nodal plane of
the
system
n
system
wing peaks in the spectrum only under the unlikely event that EaH(16A) = EaH( 16B). However, even in this event the spectrum with selective line broadening (Figure 3b) should be a 1:4:1 triplet of sharp lines rather than the 1:2:1 triplet observed. The observed effect of temperature on the ESR spectrum of 16 strongly suggests that a pair of equivalent conformations (topomers) are involved as is the case for 15, 2, or the 6,6-dimethyl-6-silacycloheptane-1,2-semidione wherein achiral diastereotopomers possessing a plane of symmetry are observed. The observed spectra can be nicely accommodated by conformational equilibrium between the superimposable structures 16C and 16D.
16C
16D
H, and H, are in the nodal H, and H , are in the nodal plane of the
R
system
plane of the n system
Each of these chiral topomers contains four different a-hydrogen atoms, but equilibration between them time averages H(1) with H(4) and H(2) with H(3) to give the observed triplet of triplets at +50 "C (Figure 3a). The wing peaks will remain sharp irrespective of the rate of interconversion because both topomers contain the same ensemble of a-hydrogen atoms. A 1:2:1 triplet of sharp lines can occur in the low-temperature spectrum with selective line broadening, if the ESR spectrum for conformationally frozen 16C,D contains fortuitous overlap a t the center of the spectrum to give a line of intensity two whose ESR (12)Unpublished work with C. E. Osuch.
transition does not change in energy when H(1), H(4) and H(2), H(3) are interchanged. The only possibility for this situation is the overlap of the lines with nuclear spin orientations a,p,p,a and p,a,cy,p where the four spins are arranged in order of decreasing uH. The hydrogen atoms H(2) and H(4) most removed from the nodal plane of the spin label will have hfsc greater than hydrogen atoms H(1) and H(3).13 To explain the observed spectrum, the ordering of these hfsc must be H(2) > H(4) > H(1) > H(3). Only in this case does the conversion of 16C to 16D (which converts H(2) to H(3) and H(1) to H(4)) have no effect on the energies of the a,p,p,a and p,cy,a,p states. Conversion of 16C to 16D converts the a2,p4,p1,a3 spin state in 16C to the isoergic ff&,p4,ctyZ spin state in 16D, while the &,cy4,a1,p3state in 16C is converted to the isoergic p3,a1,a4,p2 state in 16D. At temperatures below -30 "C, 16 gives a spectrum which is not inconsistent with structure 16CD (four doublet splittings), but broadening of the lines and the possibility for asymmetric ion pairing in a trans semidione12 eliminate the possibility of a definitive analysis.
Experimental Section
"4
b-
H,
c--.
.
J . Org. Chem., Vol. 44, No. 15, 1979 2783
Cyclononane-l,2-~emidione was prepared by mixing equal volumes of a solution of the 1,2-bis(trimethylsiloxy)cyclononene (0.1 M) with potassium dimsylate (0.2 M) in Mea0 in an inverted H cell which had been thoroughly deoxygenated by prepurified nitrogen.I4 The 6,6-dimethyl-6-silacyclononane-1,2-semidione was prepared in a similar fashion from the a-hydroxy ketone.15 For low-temperature studies, the semidiones were prepared in DMF using potassium tert-butoxide (0.5M). The g values were
measured using a dual cavity with a Varian V-4500 spectrometer. Semidione 7 was prepared from the dione16 in Me2S0 by electron transfer from propiophenone in the presence of potassium tert-butoxide.13 Semidione 9 was prepared from tetracyclo[5.3.1.02~6.03~9]~ndec-4-ene17 (0.04g) by treatment with potassium permanganate in acetic anhydride to form the dione.18 The crude dione was treated with potassium tert-butoxide in Me2S0 containing propiophenone to form 9. Semidione 10 was prepared from the monoketone, tetracyclo[6.3.1.02~6.05~10]dodecan-3-one,19 by treatment with a trace of air in MezSOcontaining potassium tert-butoxide. 4,4,8,8-Tetramethylcyclononane-l,2-semidione was prepared from the corresponding acyloin20 or bis(trimethylsi1oxy)alkene obtained by acyloin condensation of 3,3,7,7-tetramethylazelaic dimethyl ester.*O
Acknowledgments. 2-Hydroxy-7,7-dimethyl-7-silacyclononanone was kindly furnished by Professor P. Mazerolles.21 The dione precursor to 7 was supplied by Professor H.-D. Scharf,lGthe olefin precursor to 9 was supplied by Professor M. Kawanishi,ls and the ketone precursor to 10 (ethanoadamantan-3-one)was supplied by Professor T. Sasaki.lg Registry No. 2, 70136-05-9;3, 70524-36-6;7, 70561-38-5;9, 70562-09-3;10, 70524-37-7;15, 70136-06-0;1,2-bis(trimethylsiloxy)cyclononene, 70524-38-8. (13)G.A. Russell and E. T. Strom, J . Am. Chem. SOC.,86,714 (1964). (14)G.A. Russell, E. G. Janzen, and E. T. Strom, J . Am. Chem. Soc., 86, 1807 (1964). (15)R. A. Benkeser and R. F. Cunico, J . Org. Chem., 32,395 (1967). (16)H.-D. Scharf, P. Friedrich, and A. Linckens, Synthesis, 256 (1976). (17)T.Katsushima, R. Yamaguchi, M. Kawanishi. and E. Osawa, Chem. Commun., 39 (1976). (18)K.B. Sharpless, R. F. Lauer, 0. Repik, A. Y.Teranishi and D.R. Williams, J . Am. Chem. SOC.,93,3303 (1971). (19)T.Sasaki, S. Eguchi, and Y. Hirako, J . Org. Chem., 42,298(1977). (20)A. T.Blomquest and G. A. Miller, J . Am. Chem. SOC.,83,243(1961). (21)P. Mazerolles and A. Faucher, Bull. SOC.Chrm. Fr., 2134 (1967); P. Mazerolles, A. Faucher, and A. Laporterie, ibid , 887 (1969).
